## PSN-L Email List Message

Subject: Re: BBC news article about infrasound
From: ChrisAtUpw@.......
Date: Sun, 16 Feb 2003 21:49:12 EST

In a message dated 16/02/03, hernlund@............ writes:

> Because the atmosphere becomes less dense approximately exponentially with
> height, the sound wave velocity decreases.

Hi John,

The velocity of sound in air is primarily proportional to the square
root of the absolute temperature, which of course decreases with height up to
the stratosphere. Pressure has relatively little effect over the atmospheric
range. Dispersion goes roughly with f^2, where f is the frequency, so waves
of a few Hz or less can propagate around the globe. Volcanic explosions may
be detected going around the Earth several times.

Regards,

Chris Chapman
In a message dated 16/02/=
03, hernlund@............ writes:

Because the atmosphere beco= mes less dense approximately exponentially with height, the sound wave veloc= ity decreases.

Hi John,

The velocity of sound in air is pri= marily proportional to the square root of the absolute temperature, which of= course decreases with height up to the stratosphere. Pressure has relativel= y little effect over the atmospheric range. Dispersion goes roughly with f^2= , where f is the frequency, so waves of a few Hz or less can propagate aroun= d the globe. Volcanic explosions may be detected going around the Earth seve= ral times.=20

Regards,

Chris Chapman

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